In the past project period, studies with MMTV-TGFbeta1($223,225) transgenic mouse lines have shown marked inhibition of ductal development and branching. Furthermore, we have generated data indicating that resistance to TGFbeta1 growth inhibition can result from c-myc misregulation. Studies with MMTV-TGFalpha transgenic lines in Coffey's laboratory have demonstrated that misregulation of TGFalpha in breast epithelial cells leads to hyperplasias and an increased incidence of spontaneous and DMBA-induced tumorigenesis. Based on this and other data, it is hypothesized that in early steps of mammary carcinogenesis, over-expression of TGFalpha promotes, and over-expression of TGFbetas retards or suppresses, the carcinogenic process. With mutations in the carcinoma cells that result in loss of TGFbeta growth inhibition, the TGFbetas then accelerate tumor progression through paracrine effects on stroma, including angiogenesis, and local immunosuppression. The specific alterations that can cause the loss of the growth inhibitory response to the TGFbetas can include c-myc misregulation. These hypotheses will be tested through the following specific aims: 1. Determine the effect of MMTV-TGFbeta1$223,225 transgene expression on mammary development and susceptibility to mammary tumor formation: (a) Continued characterization of the MMTV-TGFbeta1$223,225 transgenic mouse lines. (b) Crossbreeding of homozygous MMTV-TGFalpha and homozygous MMTV-TGFbeta1$223,225 lines to determine effect on tumor formation. (c) Determination of the effect of the MMTV-TGFbeta1$223,225 transgene expression on DMBA-induced tumorigenicity. 2. Determine the effect of expression of TGFalpha and TGFbeta1$223,225 under the control of the whey acidic protein promoter on mammary development and susceptibility to mammary tumor formation: (a) Generate transgenic lines. (b) Characterize expression and phenotype (c) Determine effect on spontaneous tumor development. 3. Determine effects of c-myc misregulation on biological effects of TGFbeta1: (a) Crossbreed myc and TGFbeta1$223,225 transgenic mice to determine effects of TGFbeta1$223,225 misregulation on myc-induced breast tumor formation, including Wap-myc vs. Wap-TGFbeta1$223,225 and MMTV-myc vs MMTV-TGFbeta1$223,225 transgenic lines. (b) Transfect c-myc constructs into BALB/MK cells and TGFbeta1-sensitive breast carcinoma cell lines and determine effects of over-expression of the respective c-myc genes on TGFbeta1 sensitivity. 4. Transgenic mouse experiments with metallothionein (MT) promoters to determine the effects of misregulating TGFbeta1$223,225 on different stages of embryonic and postnatal development.